In a typical multi-compartment refrigerator there are several methods for controlling the temperature of each of the compartments. It is common practice for the refrigeration system, i.e. the compressor, evaporator, fan, etc., to directly cool the freezer compartment. Air from the freezer compartment is directed to the fresh food compartment by means of an opening from the freezer to the fresh food compartment. Air is throttled in this opening by means of some type of air damper control. The damper has traditionally been a manually operated mechanism, which can be adjusted by the user to vary the freezer temperature. The fresh food temperature is generally controlled by a thermostat which senses the fresh food compartment temperature. The thermostat governs the operation of the compressor and evaporator fan. The resulting freezer temperature is a function of the fresh food compartment set point temperature and the position of the manual damper. It is generally known that this type of control system is not ideal for temperature stability of the freezer, especially when the outside temperature changes and the fresh food set point temperature is changed. The advantage of this system is that it is very inexpensive to produce.
A less traditional means of control used currently in only approximately 15% of standard refrigerators produced in the United States is to cycle the compressor using a thermostat that senses the freezer temperature. The air flow to the fresh food compartment is attenuated by a modulating air damper control. This control uses a refrigerant charged bellows that expands and contracts in response to the temperature of the fresh food compartment. The bellows movement is then used to drive a door, located in the air flow stream, to attenuate air flow to the fresh food compartment. The movement of the door is very predictable, thus allowing this device to be offered on a production basis. This type of control system allows for more accurate temperature control for both compartments than the method described above. Outside temperature variance and door openings are better compensated using this system.
The principal drawback for such a system is cost. Manufacturers positioning certain product as “high performance” are the users of this type of system. Further, despite the improved efficiency of this more expensive system, the controlled temperature of both compartments still varies over a substantial range of temperatures. This is due to the passive nature of both of these control functions, which is characterized by greater operating tolerances as well as limited response time. Another problem of such a damper system, which also plagues the less expensive systems, is icing of the damper door. The buildup of ice on the damper door can prevent proper operation of the temperature control. Such ice buildup may result in the damper door being prohibited from opening or closing, thus upsetting the normal control of temperature in both compartments.
The growing use of microcontroller and microprocessor based controls in residential appliances now makes them cost effective for use in residential refrigerators. They provide increased control accuracy, faster response, and lower refrigeration cycle times, all of which result in higher efficiency and lower operating costs to the consumer. Within these electronic control type systems, however, there remains a need for mechanical damper assemblies. To further improve the operating efficiency of the electronic controls these mechanical damper assemblies must preferably be capable of operating in a gated manner; i.e. in an open/closed sequence at a given duty cycle, as determined by the electronic control. The ideal damper assembly therefore must itself be capable of fast response as well as efficient air flow characteristics.
One such mechanical damper system that overcomes the problems existing with the prior systems is disclosed in U.S. Pat. No. 6,240,735, to Kolson et al., entitled ROTARY DAMPER ASSEMBLY, and assigned to the assignee of the instant application, the teachings and disclosure of which is hereby incorporated in their entireties by reference thereto. Advantageously, this patent discloses a rotary damper assembly for controlling the flow of a fluid. The rotary damper assembly includes inner and outer hollow cylinders, each having one or more side wall apertures. The inner cylinder is nested within the outer cylinder in a manner to permit relative axial rotation of the cylinders about a common longitudinal axis. This inner cylinder receives the fluid flow at an axial inlet. The flow of fluid out of the assembly is in a radial direction through the side wall apertures. The size of the opening formed by the side wall apertures is proportional to the degree of alignment of the cylinder apertures.
While the Kolson et al. rotary damper assembly provides a great advance over the prior damper systems, overcoming many of the problems existing therewith, it is designed to control the flow of fluid between two compartments. However, high end, specialty, and newer refrigerator models being designed today include multiple compartments to store fresh food. A crisper drawer or compartment inside the main fresh food compartment is one such example. While present models typically allow a user to manually set a damper between the main fresh food compartment and the crisper drawer, such temperature control suffers from the very problems that lead to the use of controlled dampers between the freezer and the fresh food compartment, e.g. wide temperature variances. This problem is especially acute with the crisper drawer or compartment as its frequency of being opened compared to the main refrigerator door of the fresh food compartment is much less. However, the temperature control is generally driven by the fresh food compartment temperature. As such, the crisper drawer may become over chilled, which may damage vegetables and fruits stored therein.
The Kolson et al. rotary damper also requires a directional change in the fluid flow through the assembly. That is, the Kolson et al. damper redirects the flow of the fluid from an axial flow to a radial flow therein. This results in increased fluid turbulence, which reduces the efficiency of the fluid exchange between the two compartments. Refrigerator manufacturers are very concerned about power consumption, and are very competitive in reducing power consumption. They are also under tremendous pressure from the Department of Energy to make incremental power consumption reductions. As such, any improvements in the efficiency of any aspect of the refrigerator is highly sought after.
Therefore, there continues to exist a need in the art for a damper system that provides better temperature stability of all of the temperature controlled compartments of a refrigerator, including the freezer compartment, the fresh food compartment, and the crisper drawer or compartment, while reducing the cost and power consumption and increasing the overall efficiency of the system.